SEISMIC RISK ZONES

Most local jurisdictions measure seismic risk based on seismic zones established by code, such as the Uniform Building Code with its 4 risk zones [1=low to 4=high]. There are also maps, such as this one, which identify the Effective Peak Acceleration (EPA) which further reflect the light, moderate, and severe shaking risks as a percentage of the acceleration of gravity that can be expected in an area.

In the United States, the greatest activity areas are the western states, Alaska, and some volcanic island areas. However, noted historical earthquakes occurred in Massachusetts (1755), Missouri (1811), South Carolina (1886), and Alaska (1964). The Caribbean Islands and Puerto Rico have been sites of severe earthquakes. The history of earthquakes in the United States has been recorded for over 200 years and new areas of concern include moderate risk areas in southern and mid-western states.

The Richter Magnitude Scale, first published in 1935, records the size of an earthquake at its source, as measured on a seismograph. Magnitudes are expressed in whole numbers and decimals between 1 and 9. An earthquake of a magnitude of 6 or more will cause moderate damage, while one of over 7 will be considered a major earthquake. It is important to remember that an increase of one whole number on the Richter Scale is a tenfold increase in the size of the earthquake.

The Federal Emergency Management Agency

The Federal Emergency Management Agency -- FEMA -- is an independent agency of the federal government, reporting to the President. Since its founding in 1979, FEMA's mission has been to reduce loss of life and property and protect our nation's critical infrastructure from all types of hazards through a comprehensive, risk-based, emergency management program. FEMA works with the state and local governments and the private sector to stimulate increased participation in emergency preparedness, mitigation, response and recovery programs related to natural disasters. To minimize damage-repair-damage cycles, FEMA carries out and encourages preventive activities referred to as hazard mitigation.

The FEMA Hazard Mitigation Program, established in 1988 with the passage of the Robert T. Stafford Disaster Relief and Emergency Assistance Act, offers a framework for protecting historic structures from natural disasters. In the event of a federally declared disaster, state and local governments as well as eligible non-profit applicants may receive financial and technical assistance to identify and carry out cost-effective hazard mitigation activities.

FEMA encourages hazard mitigation projects, including the restoration of buildings, by providing technical assistance and funding through the Hazard Mitigation Grant Program (HMPG), which can underwrite up to 50% of the cost of the project.

FEMA's public-assistance program provides financial and other assistance to rebuild disaster-damaged facilities that serve a public purpose, such as schools, hospitals, government buildings and public utilities.

In terms of technical assistance, FEMA, under a cooperative agreement with the Building Seismic Safety Council has produced two volumes of comprehensive material dealing with the seismic retrofit of existing buildings (see Further Reading). In addition an ongoing project ATC-43 involves earthquake analysis procedures for Unreinforced Masonry Buildings and Reinforced Concrete Buildings. These documents contain nationally applicable technical criteria intended to ensure that buildings will withstand earthquakes better than before. There is a great deal of information that is applicable to historic buildings, although historic buildings are not necessarily identified as a category. Write for FEMA publications at:

FEMA, PO Box 70274, Washington, DC 20024

For current information about emergency activities, federally declared disaster areas, or how to contact regional offices see the FEMA website: http://www.fema.gov/